Electronic metering device including automatic service sensing

ABSTRACT

An integral electronic meter system diagnostics package including a microprocessor, storage memory, pre-select series of system diagnostic tests, and recording any results which exceed predefined programmable thresholds, and display means for displaying error and/or diagnostic messages identifying selected diagnostic data and/or errors discovered in the meter tests during a predefined period. The system automatically senses the type of electrical service in which the meter is installed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of Ser. No. 08/037,938, nowU.S. Pat. No. 5,469,049, for "System Checking and TroubleshootingPackage for an Electric Metering Device," filed Mar. 26, 1993.

TECHNICAL FIELD

The present invention relates to an integral method and apparatus forconducting system installation diagnostics in a solid state electronicmeter.

BACKGROUND ART

Induction-type watt hour meters typically employ a pulse initiator whichgenerates pulses in proportion to the rate of rotation of a meter disk.These generated pulses are transmitted to electronic registers forderiving current, voltage, power and/or time of use energy consumption.

Various types of solid state polyphase electronic meters are also incommon use today. These meters, which monitor electrical energyconsumption and record or report such consumption in kilowatt hours,power factor, KVA, and/or reactive volt amperes, typically employ solidstate components, and may utilize analog-to-digital converters toprovide digital data rather than pulse data from which variousdemand/consumption indicators can be extracted.

It is also well known to provide solid state electronic meters which maybe configurable for installation in any one of a variety of single ormulti-phase electricity distribution systems. One example of a solidstate electronic watt hour meter is disclosed in U.S. Pat. No.5,059,896, issued to Germer et al.

Art example of a solid state electricity demand recorder which may beused in conjunction with a conventional watt hour meter is disclosed inU.S. Pat. No. 4,697,182, issued to Swanson.

Various ancillary equipment and diagnostic techniques are utilized byservice personnel during installation of these meters in attempting toconfirm that the installation has been wired correctly. However, manyinstallation checks, such as polarity and cross-phase checks, arederived on site by field personnel and are therefore dependent upon theknowledge and competence of those personnel.

While various diagnostic equipment is available for use by fieldpersonnel during installation and periodic maintenance, a need existsfor an integral apparatus which automatically and periodically performsa standard series of system and installation diagnostics withoutinterrupting the operation of the meter. In addition, there is a needfor periodic self-checks of the meter to determine and record theoccurrence of selected pre-defined fatal and non-fatal errors in themeter's operation.

In addition, although there are meters available which may be adaptedfor use in more than one type of electrical service, one drawback ofthese meters is that the customer often must program the service typeinto the meter prior to installation. This pre-installation programmingof multiple service meters tends to limit their multiple servicecapability.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide an integralsystem checking and troubleshooting package for a solid state electronicmeter.

It is another object of the present invention to provide a method andapparatus which is integral with a solid state meter and whichautomatically performs a series of predefined system installation anddiagnostic tests on the meter.

It is still another object of the present invention to provide a systemchecking and troubleshooting package which supports and is integral toan electronic meter, and which includes means for displaying the resultsof selected self-checks and system diagnostic tests when interrogated byservice personnel.

It is yet another object of the present invention to provide anautomated system checking apparatus which periodically checks for theexistence of certain pre-defined conditions and which, depending uponthe nature of the error, takes predefined action in response to thedetection of any such errors.

It is another object of the present invention to provide a method andapparatus for determining the angles of each voltage and current phasorwith respect to a preselected base phasor, for the purpose of verifyingthat all meter elements are sensing and receiving the correct voltageand current for each phase of a multi-phase electric service.

It is yet another object of the present invention to provide a methodand apparatus which is integral with the solid-state multiple servicemeter and which automatically senses the specific type of electricalservice after the meter has been installed, and periodically during itsoperation.

In accordance with the present invention, an integral electronic meterself-checking and system diagnostics package is provided, including amicroprocessor, storage memory, logic for automatically and periodicallyperforming a preselected set of meter self-checks and recording anyerrors therefrom, logic for automatically performing a preselectedseries of system diagnostics tests, and recording any results whichexceed predefined programmable thresholds, and display means fordisplaying error and/or diagnostic messages identifying, respectively,one or more self-check errors or selected diagnostic data and/or errorsdiscovered in the meter self-checks during a predefined period.

The device of the present invention is preferably integrated into asolid state meter which utilizes an analog-to-digital converter andassociated digital sampling techniques to obtain digital datacorresponding to current and voltage for one or more phases of a singlephase or multi-phase system to which the meter is connected.

The present invention automatically performs the preselected meterself-checks, preferably once per day, and/or when power is restored tothe meter following an outage, and/or when a full meter reconfigurationis performed, to verify the continued functionability of selected metercomponents. In the preferred embodiment, for example, the device of thepresent invention checks its own memory, microprocessor, and selectedregisters in the meter to determined whether the billing data has beencorrupted since the last check. Since the corruption of billing data isconsidered a fatal error of the meter, the device of the presentinvention would generate and display an error code indicating the natureof the error, lock the display on the error code, and cease all meterfunctions (except communications functions) until the meter isre-configured.

In addition, the device also periodically checks for other, non-fatal,errors such as for register overflows, clock, time of use, reverse powerflow, and low battery errors. The frequency of error checking may varydepending upon the component and/or condition checked, as well as thepotential effect of the error on the continued operation of the meter.Once discovered, non-fatal errors may or may not lock out the displaydepending upon the nature of the error and how the particular meter isconfigured.

The present invention also periodically performs a series of preselectedsystem diagnostics tests. These tests are at installation of the meterand preferably about once every five seconds during the normal operationof the meter. In the preferred embodiment, the device conducts apolarity, cross-phase and energy flow diagnostic, a phase voltagedeviation diagnostic, an inactive phase current diagnostic, a per-phasepower factor diagnostic, and a current waveform distortion detectiondiagnostic utilizing factory-defined parameters as well as user-definedparameters which may be specified by personnel in the field atinstallation.

In conducting the polarity, cross-phase and energy flow diagnostic, thedevice of the present invention utilizes accumulated current and voltageinformation to determine the phase angle of each voltage and currentphasor (for example V_(B), V_(C), I_(A), I_(B), and I_(C)) with respectto a reference phasor (for example V_(A)) in a multi-phase system. Theproper position of each phasor for this installation is pre-defined andused as an exemplar for comparison to the calculated phase angle todetermine whether each angle falls within a pre-defined envelope. If anyone of the calculated phase angles falls outside its correspondingpre-defined envelope, a diagnostic error message may be displayed. Thisdiagnostic is particularly useful at installations since this error mayindicate cross-phasing of a voltage or current circuit, incorrectpolarity of a voltage or current circuit, reverse energy flow of one ormore phases (co-generation), or an internal meter measurementmalfunction.

The device of the present invention also preferably includes a "Toolbox"display which, when manually activated by field personnel, causes thedisplay to scroll through a list of preselected values, such as voltageand current for each phase, the angles associated with each voltage andcurrent phasor, and the numbers of occurrences of each diagnosticfailure, for review by field personnel.

In one embodiment of the present invention, the device of the presentinvention automatically senses the type of electrical service (i.e.,Single phase, three-wire Delta, four-wire Wye, or four-wire Delta) whenthe meter is installed, after a power-up, and also, preferably,periodically during the normal operation of the meter.

The system diagnostics, Toolbox display, and automatic service sensingfunctions are performed by the device of the present invention withoutinterruption in the operation of the meter except when such operation ispurposely suspended as a result of a fatal error.

The above objects and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the system;

FIG. 2 is a perspective view of a meter into which the system of thepresent invention may be integrated;

FIG. 3 is a block diagram of the meter of FIG. 2;

FIG. 4 is a flowchart of the electrical system diagnostics checks of thepresent invention;

FIG. 5 is a flowchart of a first portion of the polarity, cross phaseand energy flow diagnostic implemented by the present invention;

FIG. 6 is a flowchart of the second portion of the polarity, cross phaseand energy flow diagnostic implemented by the present invention;

FIG. 7 is a flowchart of a first portion of the phase voltage deviationdiagnostic routine implemented by the present invention;

FIG. 8 is a flowchart of a second portion of the phase voltage deviationdiagnostic implemented by the present invention;

FIG. 9 is a flowchart of a first portion of the inactive phase currentdiagnostic implemented by the present invention;

FIG. 10 is a flowchart of a second portion of the inactive phase currentdiagnostic implemented by the present invention;

FIG. 11 is a flowchart of a first portion of the per-phase power factordiagnostic implemented by the present invention;

FIG. 12 is a flowchart of a second portion of the per-phase power factordiagnostic implemented by the present invention;

FIG. 13 is a flowchart of a third portion of the per-phase power factordiagnostic implemented by the present invention;

FIG. 14 is a list of the items displayed in the Toolbox display;

FIG. 15 is a phasor diagram for a typical three-phase meterinstallation;

FIG. 16 is a graph illustrating the relationship of the wave formsrepresenting two phase quantities tracked by the system;

FIG. 17A is the first portion of a block schematic of the front-endmodule 42 of FIG. 3;

FIG. 17B is the second portion of a block schematic of the front-endmodule 42 of FIG. 3;

FIG. 18A is the first portion of a block schematic of the registermodule 48 of FIG. 3;

FIG. 18B is the second portion of a block schematic of the registermodule 48 of FIG. 3;

FIG. 19 is a first flowchart of the current waveform distortiondetection diagnostic implemented by the present invention;

FIG. 20 is a second flowchart of the current waveform distortiondetection diagnostic implemented by the present invention;

FIG. 21 is a table illustrating the meter form factors and theassociated types of electrical services which they may support;

FIG. 22 is a flowchart of a first portion of the automatic servicesensing function implemented by the present invention; and

FIG. 23 is a flowchart of a second portion of the automatic servicesensing function implemented by the present invention.

BEST MODE OF OPERATION

Referring to FIG. 1, the system of the present invention, generallydesignated as 20, includes a central processing unit 22, storage memory24 adequate for storing digital data corresponding to the periodicsamples of the voltage and current data from the voltage A/D converter26 and current A/D converter 28, respectively, logic 30 for performingthe meter self-check and system and installation diagnostics supportedby the system, and display means 32 for displaying error and diagnosticinformation.

Referring to FIG. 2, the system 20 is preferably incorporated into asolid state polyphase Kilowatt/Kilowatt-hours ("KW/Kwh") single functionmeter 34 (as illustrated in FIGS. 3, 17A-B and 18A-B and hereafterdescribed in greater detail) including a generally circular base 36,conventional molded plastic housing (not shown) to which faceplate 38 isaffixed, a meter cover 40. The meter 34 also includes conventionalcurrent sensing elements adapted for connection to existing electricalsystems.

Referring now to FIG. 3 in the preferred embodiment, the diagnosticslogic 30 for the system 20 of the present invention is incorporated intothe front-end module 42 of the meter including a microprocessor 44, an 8bit A/D converter which serves as the voltage A/D converter 26, randomaccess memory 45, which serves in part as part of the system storagememory 24, and read-only memory and EEPROM, where the system diagnosticslogic is located, at 46. The front-end module also preferably supportsother meter functions, including meter component self-checks, A/Dsampling, energy calculations, present demand, instantaneous values, anyoptional outputs, and meter communications in addition to the system andinstallation diagnostics and Toolbox display performed by the system 20of the present invention. The display in this embodiment is a liquidcrystal display 33 preferably including nine seven-segment digits, threedecimal points and a plurality of icons useful in displaying electricalsystem information normally displayed by conventional meters as well asthe diagnostic data generated by the system of the present invention,substantially as shown in FIG. 3.

The meter 34 also includes a register module 48 having a microprocessor50 including: read only memory; random access memory 51, which alsoserves in part as system storage memory; a 96 segment LCD displaydriver; and 24 I/O lines. In this embodiment, the read only memory andregister CPU 50 include the display logic for generating the Toolboxdisplay as well as the error codes generated by the system 20 of thepresent invention. The register module 48 also supports other meterfunctions such as maintaining the billing values and billing registerrelated functions, as well as time related functions includingself-read, time of use, time of operation, and mass memory.

It should be noted, that in the embodiment of the meter 34 shown in FIG.3, the system 20 of the present invention utilizes an 8 byte A/Dconverter 26 for sensing voltage signals, and an external 12 byte A/Dconverter 28 for sensing current samples. As will be appreciated bythose skilled in the art, the current converter 28 requires higherresolution since current varies over a wider range than voltage. It willalso be appreciated by those skilled in the art that it is preferable tohave separate converters for simultaneously sensing the current andvoltage so that the phase error caused by the current transformer may bedirectly compensated by adjusting the delay between the current sampleand the voltage sample. Thus, in the event the current transformer isideal and imparts no phase delay, then voltage and current can besampled simultaneously with the independent converters 26 and 28.

The display logic for generating the Toolbox display and diagnosticerror message of the system 20 is part of the display logic 52 which isimplemented by the register CPU 50 in the particular embodiment of FIG.3. It will be appreciated by those skilled in the art, however, that thelogic and CPU capabilities of the system of the present invention may beimplemented in a simpler single processor architecture (such as shown inFIG. 1), as well as the architecture shown in FIG. 3, or other hardwareimplementations without departing from the spirit of the presentinvention.

The system 20 of the present invention provides a full range of systemdiagnostic capabilities and diagnostic display functions through the"Toolbox" display. The system and installation diagnostics are definedin part by the user via the programming software. The Toolbox is adisplay of a fixed set of diagnostic information contained in a specialmode of operation that can be accessed by a user, typically fieldpersonnel, preferably by activating a magnetic switch on the meter. Eachof the diagnostic capabilities will be discussed in further detailbelow.

In one embodiment, the system 20 also provides an automatic servicesensing capability. As described in further detail below, thiscapability includes logic for automatically determining the electricalservice supported by the meter at installation, on subsequent power-ups,and periodically during the operation of the meter, based upon thepre-programmed form number of the meter and the angular displacement ofvoltage vectors Va and Vc, which are automatically periodicallydetermined by the system as described below.

System and Installation Diagnostics

The system 20 of the present invention performs a plurality of systemand installation diagnostics which may indicate potential problems withthe electrical service, the incorrect installation of the meter, orinternal meter malfunctions. Although these diagnostics may varydepending upon the type of electrical service supported by the meter,the below-described diagnostics are typically performed by the system.

Referring to FIG. 4, the system and installation diagnostics are alsopreferably implemented as a state machine. In the preferred embodiment,the diagnostics consist of four diagnostics that the user may choose forthe meter to perform--(1) Polarity, Cross Phase and Energy Flow Check;(2) Phase Voltage Deviation Check; (3) Current Transformer Check; (4)Per-Phase Power Factor Check; and (5) Current Waveform Distortion Check.All selected diagnostics are performed by the meter at least once every5 sample intervals.

When any error condition occurs according to the parameters defined bythe user corresponding to the failure of a diagnostic, the meterdisplays information to indicate the error condition, and optionallytriggers an output contact closure, such as a mercury wetted relay or asolid state contact programmed as an "Error Condition Alert." When anoptional output is programmed as an Error Condition Alert, this outputcontact will close whenever any diagnostic error that has been selectedby the user is triggered.

Referring again to FIG. 4, the system 20 of the present inventionpreferably iterates through a series of calculations and diagnosticchecks, shown at 54-62. In the preferred embodiment, processing time isdivided into sample intervals equal to 60 periods of the power lineclock. For example, in a 50 Hz installation, this is 1.2 seconds. In a60 Hz installation, the sampling interval would be 1 second.

Using a simple counter, the system 20 performs the necessary samplingand calculations to determine the angle of I_(A) (preferably relative tothe base phasor V_(A)), as well as performing Diagnostic Check #1 duringthe first interval, as shown at 54.

In the second interval, at 56, the system 20 accumulates the necessarysamples to calculate the angle for I_(B) and performs Diagnostic Check#2.

In the third interval, at 58, the system accumulates the necessarysamples to calculate the phase angle for I_(C) and performs DiagnosticCheck #3.

In the fourth interval, at 60, the system accumulates the necessarysamples to calculate the phase angle for V_(B) and performs DiagnosticCheck #4.

In the fifth sample interval, at 62, the system accumulates thenecessary samples to calculate the phase angle for Vc, performsDiagnostic Check #5, and sets the counter to zero.

The counter is incremented (at 64) at the end of each of theseintervals, and the sequence is repeated continuously. Thus, in a 60 Hzsystem, the phase angle for each of the current and voltage phasors iscalculated, and each of the four diagnostic checks are performed, onceevery 5 seconds. As will be appreciated by those skilled in the art,different time intervals can be implemented and/or the sub-routines of54-62 can be modified to accommodate more frequent or infrequent checksof one or more of the selected diagnostics as desired.

DIAGNOSTIC #1--Polarity, Cross Phase and Energy Flow Check

Referring to FIGS. 5 and 6, the Polarity, Cross Phase and Energy FlowCheck is designed to check for reversed polarity of any phase voltage orcurrent, and to check for voltage from one phase being incorrectly wiredto the current from a different phase. This condition may also resultfrom the presence of cogeneration. This check is accomplished byperiodically measuring the angle for each voltage and current phasorwith respect to a reference phasor (preferably V_(A)). Each angle iscompared to its ideal angle, defined as the angle which would resultfrom a balanced, purely resistive load. If any voltage angle is laggingor leading its ideal angle by more than a predefined amount, (preferably10°), or if any current angle is lagging or leading its ideal angle bymore than a second predetermined amount (preferably 90°), the meterindicates a Diagnostic #1 error.

As shown in FIG. 5, the Polarity, Cross Phase and Energy Flow Checkdiagnostic routine 66 of the system 20 first checks each angle (whereapplicable for the particular electrical system to which the meter isconnected) of each of the current and voltage phasors (at 68-76) todetermine whether each is within tolerance of the predetermined idealfor an ABC rotation. If any of the angles are not within tolerance ofthe ideal, the system sets the abc flag false (at 78) and proceeds (asshown in FIG. 6) to check each of the angles, assuming a CBA rotation.

If all of the angles are determined at 68-76 to be within tolerance oftheir predetermined ideal, the system 20 sets the abc flag true, at 80,and proceeds to check the angles assuming a CBA rotation.

Referring now to FIG. 6, once the ABC rotation check is performed, thesystem proceeds at 82-90 to check the angles for each of the current andvoltage phasors to determine whether, for a CBA rotation, the phaseangles are within tolerance of the predetermined ideal angles. If anyone of the phase angles is outside of the range of tolerance for thepredetermined ideal angle for that phasor, the system sets the cba flagfalse, at 92. If all of the phase angles are determined to be withintolerance of the predetermined ideal angles, the system sets the cbaflag true, at 94. The system 20 then determines whether either the abcor the cba flag is true. If either is true, this diagnostic check ispassed. If neither the abc flag nor the cba flag is true, the diagnosticcheck has failed for both ABC and CBA rotations, indicating a diagnosticerror.

When a diagnostic error is determined, the system records the occurrenceof the error and displays the error as further described hereinafter. Inthe preferred embodiment, however, the initial display of thisdiagnostic error will not occur until the error condition has beenpresent for three consecutive checks.

As will be appreciated by those skilled in the art, this diagnostic mayindicate one of several problems, including cross phasing of a potentialor current circuit, incorrect polarity of a potential or currentcircuit, reverse energy flow of one or more phases, or internal metermeasurement malfunction.

DIAGNOSTIC #2--Phase Voltage Deviation Check

Referring now to FIGS. 7 and 8, the Phase Voltage Deviation Check isdesigned to check, at 98, for any phase voltage being outside anenvelope defined by the user. This is actually a check of thedistribution transformer voltage gap. This check is accomplished byperiodically measuring the voltage for each phase and checking itagainst a predefined voltage envelope referenced by the programsoftware.

The formula used for this check is: ##EQU1##

If any phase voltage is above V_(upper) or below V_(lower), the meterwill indicate a Phase Voltage Envelope Diagnostic Error.

It should be noted that in the preferred embodiment, the system 20checks, at 100, to determine whether the electrical service supported bythe meter incorporating the system 20 is a three element, four wiredelta service. If so, the system calculates special case upper and lowerbounds for the phase C voltage, as shown at 102.

Again, if either of the phase B or phase C voltages exceeds thepredetermined bounds, the system indicates the failure of thisdiagnostic check (at 104 or 106), indicating a diagnostic error, and theerror is recorded and the appropriate error message is displayed ashereinafter described. Otherwise, this diagnostic check is passed (at108) and this check is completed.

It should be noted, however, that in the preferred embodiment, theinitial display of this diagnostic error will not occur until the errorcondition has been present for three consecutive checks.

This diagnostic may indicate a loss of phase potential, incorrectpotential transformer ratio, shorted potential transformer windings,incorrect phase voltage, and internal meter measurement malfunction, aswell as other potential problems.

DIAGNOSTIC #3--Inactive Phase Current Cheek

Referring now to FIGS. 9 and 10, in performing the Inactive PhaseCurrent diagnostic, the system 20 will periodically compare theinstantaneous RMS current for each phase to a predefined minimum currentlevel, which is preferably selectable from 5 ma to 200 A in incrementsof 1 ma. If all three phase currents are above the acceptable level, orall three phase currents are below the acceptable level, this diagnosticwill pass. Any other combination will result in a Diagnostic #3 failure,and a Diagnostic #3 error will be indicated.

Again, however, the recording and display of this diagnostic error willpreferably not occur until the error condition has been present forthree consecutive checks.

The occurrence of a Diagnostic #3 error signifies the existence of amagnitude error with one or more of the meter phase currents. In orderto determine the specific problem, the user must obtain the phasecurrent information from Toolbox Mode, as described hereinafter.

It will be appreciated by those skilled in the art that this diagnosticcheck can be utilized to indicate any one of several potential problems,such as an open or shorted current transformer circuit.

DIAGNOSTIC #4--Per-Phase Power Factor Check

Referring to FIGS. 11-13, the Per-Phase Power Factor Diagnostic Check isdesigned to verify that, for each meter phase, the angle between thecurrent phasor and the idealized voltage phasor is within an envelopespecified by the user (±1-90'). Since this tolerance is more restrictivethan for Diagnostic #1, the system 20 does not perform this diagnosticcheck until Diagnostic #1 has passed. This diagnostic may indicate anyone of a series of potential problems, including poor load power factorconditions, poor system conditions, or malfunctioning system equipment.

The system 20 first checks the abc and cba rotation flags at 114 and116. If both of these flags are false, this indicates that Diagnostic #1has failed. Since the tolerances of this diagnostic are more restrictivethan Diagnostic #1, the diagnostic check is aborted.

If either the abc or cba flags are true (indicating that Diagnostic #1has passed), the system 20 performs the appropriate ABC or CBA rotationchecks at 114 and 116, respectively. For an ABC rotation, the systemchecks the angle between the appropriate current phasor and theidealized voltage phasor, at 118-122, to determine whether the angle iswithin an envelope specified by the user. If the angle is between thepredetermined envelope, the diagnostic is passed at 124. If not, thediagnostic is failed (at 126), indicating a Diagnostic #4 error. In theevent of a CBA rotation, the system 20 performs similar envelope checksat 128-132 for the applicable current phasor.

DIAGNOSTIC #5--Current Waveform Distortion Check

Referring to FIG. 19, the Current Waveform Distortion Check is designedto detect the presence of DC current on any of the phases. Thisdiagnostic is particularly useful on meters which are designed to passonly alternating current, and where performance of the currenttransformer degrades with enough direct current, since the directcurrent biases the transformer so that it operates in a non-linearregion.

The principal way of generating direct current on a meter is by placinga half-wave rectified load in parallel with a normal load. The presenceof the half-wave rectified current signal has the effect of heighteningeither the positive or negative half cycle of the waveform while leavingthe other one unaffected. For those meters which are not designed topass direct current, when this signal appears at the input of thecurrent transformer it is level shifted so that the output has anaverage value of zero. However, the peak of the positive and negativehalf cycles of the wave no longer have the same magnitude. The directcurrent detection diagnostic exploits this phenomenon by taking thedifferences of the positive and negative peak values over a samplinginterval of the meter. The result of the accumulation of the currentsamples over an interval should be a value near zero if no directcurrent is present. If direct current is present, then the accumulatedvalue will be significantly higher. This method, referred to hereinafteras the Comb Filter Method, yields accurate values regardless of thephase and magnitude of the accompanying alternating current waveform.

Since the meters employing the present invention are typicallypoly-phase meters, meaning that there are two or three phase currentsmeasured by the meter, it is possible for someone to tamper with themeter by adding a half-wave rectification circuit across the load tointroduce direct current into the installation. This circuit could beadded on a single phase. For this reason, the DC detection diagnosticshould be enabled to detect direct current on a per-phase basis.

The Comb Filter Method of calculating a direct current detection valueper phase is illustrated in the flowchart of FIG. 19. The methodinvolves the following steps during each sample interval:

(1) The sign of the first voltage sample in each interval is recorded;

(2) Using the sign of the first voltage sample, the first voltage zerocrossing is detected;

(3) Accumulate the second sample of current after the voltage zero crossover into the current peak accumulator (this is approximately 90°) ;

(4) Accumulate every fourth current sample after the initial currentsample into the current peak accumulator (approximately 180° apart);

(5) Repeat step 4; and

(6) At the end of the sample interval, divide the accumulated currentpeak values by the appropriate current being used during the interval.This has the effect of normalizing the result for three different gainranges that exist for the current. Also, zero the accumulator for thenext sample interval.

The result of the division in step 6 is a unitless value which isdirectly proportional to the amount of direct current present on thatphase. This value will be referred to as the DC Detection Value. The DCDetection Value is compared to a preselected Detection Threshold Valueto determine whether direct current may be present. In the preferredembodiment, the Detection Threshold Value is set to 3.000, since it hasbeen found that a value of 3.000 is a suitable threshold for both 200amp and 20 amp meters.

This diagnostic utilizes A/D sampling to ascertain the voltage andcurrent from each phase, sampled 481 times for each sample interval(typically 1 second). The current for each phase has a gain associatedwith it. This gain can change every sample interval if the magnitude ofthe current is changing fast enough. This fact is important in detectingdirect current, since the detection technique will require the summingof sampled current values over some length of time. If a time periodgreater than the sample interval is chosen, then the possibility existsthat the sum of current values includes samples taken at different gainranges, and thus the accumulated samples lose their meaning. Thus, it isimportant that the resulting accumulated current peak values benormalized by the appropriate current gain used during each interval asspecified in step (6) above.

It should be noted that the calculation of a DC Detection Value willonly occur for one phase during any single sample interval. Thus, unlikethe other diagnostics which are preferably performed by the meter atleast once every 5 sample intervals (typically every 5 seconds), each ofthe possible three phases is checked three consecutive times, at 5second intervals, for a total sampling time of 15 seconds per phase.Thus, the total length of time required for a complete Current WaveformDistortion Check is 45 seconds (15 seconds for each of phase A, phase B,and phase C).

If the DC Detection Value is found to be greater than the selectedDetection Threshold Value for all three consecutive intervals for aparticular phase, then direct current will be recorded as present onthat phase. After all three phases have been checked, if direct currentwas recorded on any phase, then the diagnostic is turned on. When a 45second internal has passed in which no failure was found on any phase,then the diagnostic will be turned off.

It will be appreciated that the Detection Threshold Value should be setat a level which corresponds to the level of direct current for whichthe current transformer on the meter begins to degrade, so that aDiagnostic #5 failure can be detected and recorded before this level ofdirect current is reached.

Referring to FIG. 20, the diagnostic calls the Phase Check routine threetimes for each of the three phases. The Phase Check routine thenaccumulates current samples, normalizes the accumulated samples andstores the value as a DC Detection Value DV_(n), for each of threesample intervals for that phase.

Referring again to FIG. 19, the Check DIAG #5 Routine begins at 200 byclearing the interval count and each of the phase A, phase B and phase Cerror counts (PHA ERRCT, PHB ERRCT, and PHC ERRCT). The interval countermay be a modulo 9 counter which may be incremented from the value 0-8,then back to 0, etc. For each of the first three 5 second intervals(i.e., interval count=0, 1 or 2), the routine performs a Phase Check, at202, for phase A. For the next three 5 second intervals (i.e., intervalcount=3, 4, or 5), the routine performs a Phase Check, at 204, for phaseB. And, for the final three 5 second intervals (i.e., interval count=6,7, or 8), of the 45 second diagnostic cycle, the routine performs aPhase Check, at 206, for phase C.

Upon completion of each Phase Check routine for phase A, the systemdetermines, at 208, whether the DC Detection Value is greater than theDetection Threshold Value, and increments the phase A error counter(Phase A ERRCT) if the DC Detection Value is greater than the threshold.The Phase Check routine is then called three times for phase B. Again,after each Phase Check routine is completed, the system, at 210,determines whether the DC Detection Value is greater than the DetectionThreshold Value and sets the phase B error counter (Phase B ERRCT)accordingly. The Phase Check routine is then called for phase C. Again,the system, at 212, compares the developed DC Detection Value for phaseC to the Detection Threshold Value and increments the error counter(phase C ERRCT) for phase C accordingly.

The system then determines, at 214, whether any of the phase A, phase B,or phase C error counters is equal to 3. If so, a DC current has beendetected on that phase for three consecutive sampling intervals, thesystem, at 216, notes a Diagnostic #5 failure, phase A, phase B or phaseC failure counter (PHA CHK FAILURE, PHB CHK FAILURE, or PHC CHK FAILURE,respectively), for each phase for which ERRCT=3. In any event, each ofthe PHA, PHB, and PHC CHK FAILURE counters are added to the Diagnostic#5 counter, at 218, (indicating the total accumulated number of DAIG #5failures) and the diagnostic is completed.

Thus, at the end of a 45 second sample interval, after each phase hasbeen checked three times, a Diagnostic #5 failure will be recorded ifany one of the three phase error counters has registered failures on allthree checks. The Diagnostic #5 counter (DIAG #5 ERROR COUNTER) reportedin the Tool Box mode will be a sum of the three per-phase DC detectioncounters.

Automatic Service Sensing

In one embodiment of the invention, the system includes logic forautomatically determining the electrical service supported by the meterbased upon the pre-programmed form factor of the meter and the angulardisplacement of voltage vectors V_(a) and V_(c). This capabilityeliminates the need for the customer to program the electrical servicetype into the meter in advance of installation and, thereby, allows thecustomer to take full advantage of the flexible, multi-servicecapability of the meter and reduce the customer's meter inventoryrequirements. In addition, the automatic electrical service sensingcapability ensures that the meter and any of the enabled system andinstallation diagnostics will operate correctly upon installation withminimal pre-programming. Finally, the auto-service sensing capabilityallows for re-installation of a meter from one electrical service toanother without the need to pre-program the change in the type ofelectrical service supported by the meter.

Referring to FIG. 21, in one embodiment, the system includes anautomatic electrical service Sensing capability for those meters whichhave been pre-programmed as forms 5S, 6S, 9S, 12S, 16S, 26S, 5A, 6A, 8A,and 10A. Each of the different services within one of the form groupsshown in FIG. 19 has a unique balanced resistance load phasor diagramwhich shows the angular location of each of the individual phase currentand voltages with respect to A phase voltage. In a real worldapplication, the current phasors will be removed from these balancedresistance load locations because of varying loads. However, the voltagephasors do not vary with load and should be within one or two degrees oftheir balanced resistive load locations. Since the B phase voltagephasor will not be present on the two element meters, nor on the 6S (6A)meter, this voltage is contrived. However, the phase C voltage phasor ispresent on all of the different forms and services and is measured withrespect to the phase A voltage. Thus, for the form meters identified inFIG. 21, a check of the phase C voltage phasors angular locationrelative to the A voltage phasor will alone provide the informationnecessary to determine what service the meter is in.

The lone exception to this rule is that network and four-wire WYEservice cannot be distinguished on the 5S, 5A, 26S form group by simplyexamining the phase C and phase A voltage phasor locations. In theembodiment of the system described herein, the system simply assumes afour-wire WYE service under these conditions.

Thus, as shown in FIG. 21, if the form factor of the meter is known, thetype of electrical service can often be determined by measuring theangular displacement of the voltage factors. In particular, each ofmeter forms 8A, 10A, 9S and 16S supports the four-wire WYE and four-wireDelta electrical services. Since the displacement of the voltage phasorsV_(a) and V_(c) in four-wire WYE and four-wire Delta systems isdifferent (120° and 90°, respectively, for an ABC rotation), the system,after a suitable time lag after start-up to ensure valid angularmeasurements for the phasors calculated by the system, determines thedisplacement between the V_(A) and V_(C) voltage phasors and, based uponthat displacement, determines whether the meter is installed in afour-wire WYE or a four-wire Delta system.

Similarly, for meter forms 6S or 6A, the system determines whether thedisplacement of the V_(a) and V_(c) phasors is within an acceptablerange from 120°, preferably plus or minus 10°, to ensure that the meteris installed in the appropriate four-wire WYE electrical service whichit supports. For 12S meters, the system determines whether the angle ofthe V_(a) and V_(c) phasors is within an acceptable threshold of 60°,120°, or 180° and, if so, determines that the meter has been installed,respectively, in a three-wire Delta, network, or Single phase electricalservice. Finally, for 5S, 5A, and 26S forms, the system examines theV_(a) and V_(c) phasors to determine whether their angle falls withinacceptable thresholds for each of the three-wire Delta (60°) , four-wireDelta (90°), or four-wire WYE (120°) services and, if so, records thecorresponding electrical service type.

It should be noted that in the case of the 5S, 5A, and 26S forms, thesystem cannot distinguish between four-wire WYE and Network services,since the angle between V_(a) and V_(c) phasors for both of theseservices is 120° in the ABC rotation. Since, however, not many utilitiescurrently use the 5S in a Network service, in one embodiment, the systemmerely assumes that a 120° V_(a) /V_(c) angular displacement is afour-wire WYE electrical system. It will be appreciated that if themeter is actually being used in a Network service, the meter will stillfunction correctly despite a determination by the auto-service sensingcapability that the meter is installed in a four-wire WYE network.However, since there is a 30° phase shift between current (I) andvoltage (V) in the four-wire WYE and since the current and voltagephasors in the Network service are not shifted relative to each other,some diagnostic calculations, such as diagnostics 1 and 4 describedherein, may falsely indicate errors if a 5S, 5A or 26S form meterincluding the above-described automatic electrical service sensingcapability is used in a Network service.

It will be appreciated that the system may similarly be implemented toautomatically sense the electrical service in which other form metersare installed, either by examining the voltage phasors, and/or otherinformation acquired through the automatic system diagnostics.

It should also be noted that the angular displacements illustrated inFIG. 21 are for ABC sequencing. The system also preferably, checks theV_(a) and V_(c) angular displacement values for ABC rotations in makingthe electrical service determination. It will be appreciated that in aCBA rotation, the phase C voltage phasor, V_(c), would be 360° minus theV_(c) location illustrated in FIG. 21.

FIGS. 22 and 23 illustrate a flowchart of the automatic service checkingfunction employed in one embodiment of the present invention. Each timethe meter is powered-up, or whenever the system diagnostics arereconfigured, the meter will perform the system checking servicefunction. This may be triggered by initializing the service type to aninvalid value. The system, on start-up, or reconfiguration after, forexample, a power outage, will then recognize the invalid value andautomatically begin determination of a valid service type.

A diagnostic delay is set for a predetermined period, preferably about 8seconds for a meter operating at 60 Hz, to allow the meter to settle andfor valid angular measurements for the five possible phasors to becalculated. The automatic service sensing function does not, therefore,execute while this delay is active, since the V_(a) and V_(c) phasorvalues may be unreliable. After lapse of the diagnostic delay period,the automatic service sensing function is activated at the end of eachsample interval (one second for 60 Hz) until a valid service is found.If a valid service is not found and any diagnostics have been enabled inthe system, the failure to determine a valid service will be recorded asa diagnostic #1 failure. If no diagnostics are enabled, the invalidservice error will not be recorded. In one embodiment of the systememploying the automatic service sensing function, the diagnostic #1error for an invalid service is not reported on the display unlessdiagnostic #1 is enabled to scroll or lock as described herein.

As long as a valid service is not found, the diagnostics will not bechecked. Once a valid service is determined, the type of servicesrecorded in the system, the automatic service sensing ceases, and themeter begins doing diagnostic checks during each sample interval, asdescribed hereinafter, for those system diagnostics which have beenenabled.

It should be noted that in one embodiment of the present invention, theoperation of the diagnostic #1 failure when a service detection failureoccurs is slightly different than the normal diagnostic #1 failure. Ifthe service is not found immediately on the first check, then adiagnostic #1 failure is activated, provided at least one of the systemdiagnostics capabilities are enabled in the system. As soon as a validservice is found, the diagnostic #1 error will be immediately cleared.The failure will only be displayed on the meter if diagnostic #1 isenabled to scroll or lock. The failure is always recorded on thediagnostic #1 error counter, provided that one of the system diagnosticsis enabled. If none of the system diagnostics are enabled, then thefailure will not be recorded. This allows the customer an option ofshutting off any warning.

It should be noted that, in the implementation shown in FIGS. 22 and 23,the system allows a tolerance, preferably plus or minus 10°, for thelocation of the voltage phasors in order to pass the diagnostic. Thistolerance has been found to be adequate in light of the limited varianceof the voltage phasors, typically within one or two degrees of theirbalanced resistive load locations, in field operation.

User Definition of Diagnostics

The system preferably allows the user to enable or disable theperformance of any one or more of the system diagnostics duringinstallation of the meter. If the diagnostics are implemented, thesystem also provides for user-defined parameters, preferably asdescribed below.

To activate or deactivate any of the above-described diagnostics checks,the user must respond to the following types of prompts in theprogramming software for each diagnostic check supported by the system:

"DIAGNOSTIC #N DISABLE"

For each "Diagnostic N" (where N represents one of the diagnosticnumbers 1-4), the user, upon pressing the return key, gets a menu,preferably including the following options:

Disable

Ignore

Lock

Scroll

The Disable option disables the implementation of that diagnostic.

The Ignore option, if implemented, means that the diagnostic will affectthe error condition alert (as hereinafter described), but will not bedisplayed.

The Lock option, if implemented, will cause the meter display to lock onthe diagnostic error message in the event a diagnostic error isdetermined.

The Scroll option, if implemented, will cause a diagnostic error messageto be displayed, when discovered, during the "off time" between eachnormal mode meter display item.

In addition to the above prompt, the user will be prompted to programthe electrical service type (e.g., 4-wire WYE) supported by theparticular meter installation.

For Diagnostic #2, the user will also be prompted to program thetolerance for all voltages by inserting a number (preferablycorresponding to the percent tolerance) in response to the followingprompt:

DIAGNOSTIC #2 PERCENT TOLERANCE: --

For a Diagnostic #3, the user will preferably be prompted to program anacceptable minimum current level in response to the following prompt:

DIAGNOSTIC #3 MINIMUM CURRENT: --

Diagnostic #4 preferably also prompts the user to program the allowableangle difference by inserting a number (1°-90°) in response to thefollowing prompt:

DIAGNOSTIC #4 TOLERANCE ANGLE: --

If either the Lock or Scroll option was selected, the meter will displaythe following message as soon as a diagnostic error is detected:

Er DIAG N (where N=the Diagnostic #)

Also, the Number of Occurrences of this Error Counter is incremented byone whenever the error is detected. As previously mentioned, however, inthe preferred embodiment the system acknowledgement and initial displayof a diagnostic error will not occur until the error condition has beenpresent for three consecutive checks. Likewise, the error will not becleared from the display until it has been absent for two consecutivechecks.

Again, depending on how the system is programmed at installation, thedisplay will either lock on the error message, or scroll the errormessage by displaying it during the "off time" between each normal modemeter display item. Various other error display regimes may be adoptedconsistent with the teachings of the present invention.

Meter Self-Checks

The system 20 of the present invention is also preferably suitablyprogrammed to periodically perform a series of meter self-checks and, ifany errors are detected, the system will record the existence of anerror condition, display an error code corresponding to the type oferror detected, and, depending upon the type of error, take othersuitable action.

The system preferably implements a series of routines which periodicallycheck for fatal errors and non-fatal errors. Errors are classified asfatal where the detected failure may have corrupted billing data orwhere the detected failure may cause the meter to operate unreliably inthe future. The system 20 preferably conducts meter self-checks of theinternal RAM of the meter's register module, the ROM of the registermodule, the EEPROM of the register module, a spurious RESET of theregister module, and the internal RAM, ROM and EEPROM of the front-endmodule. These meter components are preferably checked whenever power isrestored to the meter following an outage or otherwise when the meter isreconfigured. If a RAM, ROM, EEPROM, front module processor error, orother fatal error, is detected, the system 20 will display apredetermined error code corresponding to the detected error, lock thedisplay on the error code until the meter is reinitialized, and ceaseall meter function except communications.

The system 20 checks for a power-down error by determining if theregister module processor has encountered a hardware RESET without firstgoing through a predetermined power outage routine. This event mayoccur, if a transient on the power line asserts the RESET linemomentarily. One method of checking for a spurious RESET is to write aspecial byte to the register EEPROM as the last step in handling anoutage. If this special byte is not present on power-up, a spuriousRESET has occurred. The system 20 will then display the power-down errorcode and cease all meter functions except communications.

The system similarly checks for RAM, ROM, EEPROM, and processor failuresin the front-end module, as described above. In the embodimentintegrated in the meter of FIG. 3, the front-end module will stopcommunicating with the register module if any front-end module fatalerrors are discovered. If the front-end module fails to communicate withthe register module for over five seconds, it is presumed that one ofthese errors has been detected, the front-end processor failure errorcode is displayed, and the 68HC11 RESET line is asserted until thefront-end module resumes normal operation.

The meter self-checks implemented by the system also preferably includea series of non-fatal errors, such as register full scale overflow,system clock, time of use (TOU), mass memory, reverse power flow, andlow battery error conditions.

For example, a register full scale overflow error will be reported ifthe peak Kw register exceeds a pre-programmed register full scale value.If this event is detected, the system displays a register full scaleoverflow error, which error will be cleared when the meter is reset orwhen the error is cleared by a predefined programming device.

A clock error will be reported if the minute, hour, date or month dataare out of a predefined range. If a clock error occurs, the TOU and massmemory options will be disabled and will cease recording interval datauntil the meter is reconfigured.

A TOU error will be reported if an internal TOU parameter becomescorrupted and contains a value outside of its predefined accepted range.If a TOU error occurs, the appropriate error code will be displayed andthe TOU option will be disabled.

A mass memory error will be reported if an internal mass memoryparameter becomes corrupted or is out of its predefined acceptablerange. If a mass memory error occurs, the appropriate error code will bedisplayed and the mass memory option will be disabled.

A reverse power flow error will be reported if the front-end moduledetects the equivalent of one complete and continuous disk revolution inthe reverse direction. This error will be reported regardless of whetherenergy is detented or undetented.

A low battery error will be reported if the LOBAT signal on the powersupply integrated circuit is asserted when its level is checked. If alow battery error is detected, the appropriate error code will bedisplayed and, as with a clock error, all TOU and mass memory optionswill be disabled. If the battery is replaced prior to any power outage,the low battery error will be cleared when the battery voltage risesabove a predefined threshold value. However, if the battery voltage wasbelow the threshold when a power outage occurred, the meter must bereconfigured to clear this error.

The system also preferably checks for register full scale overflows atthe end of each demand interval, and preferably checks for clock, TOUand mass memory errors at power up, 2300 hours, and on any type of meterreconfiguration. The reverse power flow error is preferably checked bythe system each second, and the low battery error is checked on power upand once each interval.

In the preferred embodiment of the system 20, the system allows the userto select which of the meter self-checks will be implemented. In thepreferred embodiment, if any one of the selected non-fatal errors isdetected, the system will display a predetermined error codecorresponding to the detected error during the off-time between normaldisplay item. Alternatively, the system may allow for the user toprogram the system to lock the display on the error code of any nonfatalerror, once any such error is detected. In this event, activation of aswitch by the user will cause the meter to scroll through the normaldisplay list one time and then lock back on the non-fatal error display.

It should be noted that, in the preferred embodiment, fatal error checkscannot be disabled. If any non-fatal error is not selected, it will notbe displayed or flagged.

It will be appreciated by those skilled in the art that various displayregimes may be implemented. For example, the system may be programmed tolock the display on the error code corresponding to any non-fatal errordetected until a magnetic switch is activated. Upon activation of themagnetic switch, the system may then scroll through its normal display,then lock back on the display of the non-fatal error code.Alternatively, the system could be programmed to continue to scrollthrough a predefined display list, periodically displaying any and allnon-fatal error codes.

Other meter components may similarly be periodically checked usingconventional means and assigned error codes which may be displayed whenappropriate to alert the user of possible data corruption or unreliableoperation of the meter.

Toolbox Mode

The Diagnostics Toolbox is a fixed selected set of display itemspreferably in the format illustrated in FIG. 14. In the preferredembodiment, the Toolbox display is accessed via a magnetic reed switchwhich is located at the 12 o'clock position on the meter board, and isactivated by keeping a magnet next to the reed switch for at least 5seconds. This may be accomplished by the user by placing a magnet on topof the meter.

When accessed, the Toolbox display items are each displayed individuallyas shown and in the sequence indicated in FIG. 14. Once the meter is inToolbox display mode, it will scroll through all of the Toolbox displayitems at least one time. When the magnet is removed, the meter willfinish scrolling to the end of the Toolbox display list and then revertto Normal mode operation. The TEST annunciator will flash two times persecond during the entire time the meter is in Toolbox mode.

All of the #DIAG Error counters are preferably cleared by an externaldevice, such as by a hand-held personal computer, or through normalcommunications. In the preferred embodiment, the maximum value of eachcounter is 255.

While the meter is in Toolbox mode, it continues to perform meteroperations as usual. This assures that meter operation is not affectedeven if the magnet is left on top of the meter for an extended period oftime. The system continually updates the displayed Toolbox quantities asthey change in value during the entire time the meter is in Toolboxmode.

While in Toolbox mode, the Watt Disk Emulator scrolls at the rate of onerevolution per 1.33 seconds in the direction of power flow of the phasefor which information is being displayed at that point in time. Forexample, while A phase voltage, current, voltage angle and current angleare being displayed, the Watt Disk Emulator scrolls once per second inthe direction of power flow of phase A. As soon as the phase B values(if present) are displayed, the Watt Disk Emulator reverses direction ifthe power flow in B phase is opposite that of A phase. The Watt DiskEmulator is turned off while the four diagnostic error counters aredisplayed.

Because continuous potential indication is required by the customer,three potential indicators, preferably labelled V_(A), V_(B) and V_(C),are present on the display. These indicators are "ON" as long as thecorresponding voltage is above the predefined threshold. The thresholdis preferably defined as 75% of the lowest voltage the meter is rated tooperate at. If any voltage drops below the threshold, its indicator willflash, preferably at a rate of two times per second.

When more than one error exists at the same time, the informationrelating to only one of the errors is displayed, based upon a predefinedpriority. The following priorities are established in the preferredembodiment of the system:

1. Meter Self-check errors take priority over System and InstallationDiagnostic errors.

2. Since only one System and Installation Diagnostic error can bedisplayed at a time, the highest priority error will be the one that isdisplayed using a pre-defined priority list.

If two or more System and Installation Diagnostic errors exist, thehighest priority error will be the one that is displayed and the onethat triggers the output contact closure. If this error is thenremedied, the next highest priority error that still exists will then bedisplayed and will again trigger the output contact closure. The outputcontact closure (Error Condition Alert) thus remains asserted as long asone or more of the diagnostic errors have been triggered.

As described above and illustrated in FIG. 14, the Toolbox display alsopreferably displays the instantaneous value of the current and voltagefor each phase, and their phase relationship to the voltage on phase A.With this information, the user can construct a phasor diagram whichassists in determining the correct installation and operation of themeter. This display also shows the number of diagnostic errorsaccumulated for each diagnostic since the last time the system wascleared.

An example of the desired relationship between a phasor diagram for athree phase meter installation and a Toolbox display is shown in FIGS.14 and 15, respectively. With the phase current, voltage and angleinformation given in the Toolbox display, the user should be able toconstruct a phasor diagram as shown in FIG. 15. This will allow the userto get a snapshot of the power system status, and to identify anypeculiarities or errors. As mentioned before, the Toolbox display willalso give the status of the four diagnostic counters which will providethe user with more detailed status information for the system.

Calculation of Phase Angles

In the preferred embodiment, the angle information for phase current andvoltages utilized in system Diagnostics #1 and #4, and required fordisplay in the Toolbox display, are determined from accumulated currentand voltage values for each phase, as well as the accumulated products,Q and Y (as hereinafter defined). The voltage on phase A is preferablyused as the reference (or base phasor) for the other angles. The phase Avoltage angle will thus appear as 0.0° in the display. The five otherangle values for (I_(A), I_(B), I_(C), V_(B), V_(C)) will be reportedwith respect to the voltage on phase A, and will always be given withrespect to a lagging reference.

1. The Phase Angle Between V_(A) and I_(A)

If the Power and Apparent Power are known, the Power Factor can bederived. The relationship is as follows: ##EQU2## The phase angle (θ)between voltage and current can then be calculated as follows:

θ=arccos (Power Factor)

The device of the present invention can also determine whether thecurrent is leading or lagging the voltage by examining the sign of thereactive power. If the reactive power is positive, then the current islagging the voltage, and if the reactive power is negative, then thecurrent is leading the voltage.

In the preferred embodiment, the power, RMS voltage, and RMS current arecalculated every 60 line cycles for each phase on the meter. This isaccomplished by taking 481 samples of the voltage and current over a 60cycle period. The necessary multiplications and accumulations are done,and then these values are averaged to yield the power, RMS voltage, andRMS current for a given 60 line cycles. These quantities are then usedat the end of each 60 line cycle to calculate a power factor for eachphase.

The reactive power can be calculated much the same way as the power,except that a 90 degree phase shift must be induced between the currentand voltage measurements. This phase shift can be achieved by taking thepresent current sample and multiplying it by a delayed voltage sample(stored in memory) corresponding to a 90 degree phase shift.

2. Derivation of a Generalized Phase Angle Calculation Method

As demonstrated below, the method of calculating the phase angle ofV_(A) to I_(A) can be generalized to calculate the angle between anyreference phasor (such as V_(A)) and any other phasors (such as V_(B),I_(B), V_(DC), or I_(C)).

Referring now to FIG. 16, consider two sinusoidal waves of the samefrequency, different magnitude, and phase shifted one from another asfollows:

a(t)=A cos (ωt)

b(t)=B cos (ωt-θ).

By representing the cosine argument as (ωt-θ), the implicit assumptionis that θ represents a lagging phase shift from reference a(t) to b(t).The respective position refers to whether b(t) reaches its maximum valuebefore or after a(t) with respect to time. If b(t) reaches a maximumafter a(t), then it is said to laq a(t). If b(t) reaches a maximumbefore a(t), then it is said to lead a(t).

In order to isolate the phase angle θ, the average value of the productof the two sine waves will be evaluated. This average value will bedenoted by Q. The equation for the average value is as follows: ##EQU3##where A and B represent the amplitudes of sinusoidal waves a(t) and b(t)respectively. The amplitude, X_(MAX), of a sinusoidal wave is related tothe RMS value, X_(RMS), by the following relationship ##EQU4##Therefore, ##EQU5## Substituting these relationships into the equationfor Q, the equation becomes:

Q=A_(RMS) B_(RMS) cosθor, ##EQU6## and finally, ##EQU7##

Therefore, if the average value of the product of two sine waves and theRMS values of the two individual waves is known, then the angle betweenthe two waves can be calculated. This information alone will not allowus to determine whether b(t) is lagging or leading a(t). However, if thesine of the angle θ were known, then whether the angle was a leading orlagging angle could be determined.

In order to determine the sine of the angle, consider the average valueof the products of two sinusoidal waves, where a(t) is shifted by 90degrees or π/2 radians. An expression for the shifted version of a(t) isas follows: ##EQU8## The average value of the product of a(t) and b(t)will be referred to as quantity Y. The equation is as follows: ##EQU9##Solving the integral yields the following relationship: ##EQU10##

Therefore, if the average value of the product of the two sine waves (Q)is known, the average value of the product of the sine waves with thereference wave delay shifted by 90 degrees (Y) is known, and the RMSvalue for each of the waves is known, then the phase angle can becalculated and a determination made whether the unreferenced wave islagging or leading the reference wave. The two equations which can beused to determine the magnitude of the phase angles are as follows:##EQU11## Whether the angle is leading or lagging can be evaluated byexamining the signs of the arccosine and arcsine arguments. Since apositive angle corresponds to a lagging angle, then the following istrue for determining whether the angle is leading or lagging:

Arccosine argument (+), arcsine argument (+) --Lagging between 0 and 90degrees;

Arccosine argument (-), arcsine argument (+) --Lagging between 90 and180 degrees;

Arccosine argument (-), arcsine argument (-) --Leading between 90 and180 degrees; and

Arccosine argument (+), arcsine argument (-) --Leading between 0 and 90degrees.

Therefore, if Q, Y, and RMS values for a(t) and b(t) are available thenthe phase angle between these sinusoidal waves can be determined.

The above-described technique for finding the phase angle will thusapply to any pair of voltages or currents. For instance, to determinethe angle between V_(B) and V_(A), the two required quantities that willhave to be calculated are the average value of the product of two waves(Q_(VAB)), and the average value of the product of the two waves withV_(A) shifted by 90 degrees (Y_(VAB)).

As previously mentioned, the meter incorporating the preferredembodiment of the system 20 samples V_(A) and V_(B) 481 times every 60line cycles. If the product of V_(A) and V_(B) is calculated for each ofthe 481 samples and accumulated over a sample interval, then at the endof the sample interval the average value of the product of the twowaves, Q_(VAB), can be calculated. The equation for Q_(VAB) is asfollows: ##EQU12## where C is a calibration scaling factor used tocompensate for the reduction of the phase voltages to a measurablelevel.

Y_(VAB) can be found in a similar fashion from: ##EQU13## where the Cfor the Y_(VAB) calculation is the same as the C for the Q_(VAB)calculation and V_(A)(n-2) is the voltage V_(A) two samples previous tothe sample, V_(A)(n).

The sampling is designed so that two consecutive samples of a signal are44.91 degrees apart. Therefore, if the voltage sample from the twosamples ago is taken, this will result in a phase shift of 89.82 degreeswhich is approximately 90 degrees.

It should be noted that instead of using shifting samples of V_(A), theother quantities could be shifted by 90° to calculate the phase angle.This will result in the same results for the magnitude of the Y value.However, this will change the sign information because the phase angleis shifted by 180°. With this implementation, the following signrelationships between the arcsine and arccosine arguments exists:

Arccos (+), arcsine (-) --Lagging angle between 0 and 90 degrees;

Arccos (-), arcsine (-) --Lagging angle between 90 and 180 degrees;

Arccos (-), arcsine (+) --Leading angle between 90 and 180 degrees; and

Arccos (+), arcsine (+) --Leading angle between 0 and 90 degrees.

If the new values were to be calculated every sample interval for thephase angles needed for the Toolbox display, then the ten product andaccumulation terms shown above would have to be calculated every sampleinterval. Due to the excessive use of processor time and RAM required toaccumulate all ten terms every sample interval, only one pair of termsis preferably considered for each sample interval. This limits the useof processor time and RAM, and it makes new phase angle values availablefor the Toolbox display every five sample intervals.

In the preferred embodiment, the product terms are calculated andaccumulated in the following order:

1. First sample interval--V_(A) *I_(A) and V_(A)(-90°) *I_(A) for phaseangle I_(A) ;

2. Second sample interval--V_(A) *I_(B) and V_(A)(-90°) I_(B) for phaseangle I_(B) ;

3. Third sample interval--V_(A) *I_(C) and V_(A)(-90°) *I_(C) for phaseangle I_(C) ;

4. Fourth sample interval--V_(A) *V_(B) and V_(A)(-90°) *V_(B) for phaseangle V_(B) ; and

5. Fifth sample interval--V_(A) *V_(C) and V_(A)(-90°) *V_(C) for phaseangle V_(C).

After the fifth sample interval, the sequence begins again, accumulatingthe necessary Q and Y values for phase angle I_(A). The samples forV_(A) are stored during each sample interval. This thus requires thattwo additional values be stored for V_(A) at each interval, the twoprevious V_(A).

In the preferred embodiment, these functions are implemented in 68HC11assembly code. The multiplication and accumulation of these productterms occurs in the front-end sampling interrupt routine. The voltagevalues are 8-bit values and the current values are 12-bit values. SinceV_(A) is always involved in any of the multiplications, this will meansome of the multiplies will be 8×8 bit and some will be 8×12 bit. Sinceit is desirable to use the same algorithm to do all the multiplications,the 8-bit values are extended to 12-bit values such that an 8×12 bitmultiplication algorithm is used exclusively in the preferredembodiment.

The 8-bit voltage values for V_(B) and V_(C) are sign extended to 12-bitvalues so that all the multiplication and accumulation of product termsfor finding the phase angles are handled by two algorithms, one for theaccumulation of product terms for the Y value and one for theaccumulation of product terms of the Q value. The sign extension ofvoltage values V_(B) and V_(C) are performed during every sample period.This makes special checks unnecessary for identifying the sampleintervals in which these quantities are needed, because they areavailable during every sample interval.

All 12-bit values for current and voltages are preferably stored in16-bit registers in the memory, because the memory is segmented intobyte boundaries.

The front-end sampling routine must have a way of identifying whichproduct term is to be calculated at each sample interval. A counteridentifier is preferably utilized as an index to access the correctvalue for the multiplications necessary in the accumulation of the Q andY values.

In order to accumulate the two product terms, two accumulators are setaside in the memory map. The size of each of these accumulators is thesame, since both are doing 8×12 bit multiplies. The largest possibleaccumulated value is as follows:

Largest 8 bit value=128

Largest 12 bit value=2048

Largest accumulated result=481*128*2048=07 84 00 00 (hex)

Therefore, each accumulator is four bytes long to accommodate the worstcase result. Two four-byte accumulators are therefore set aside toaccumulate each pair of product terms for each sample interval.

At the end of each sample interval, the results in the two four-byteaccumulators are stored in two four-byte holding areas to awaitprocessing by the background routines necessary in completing the anglecalculation during the next interval.

Once the accumulated pairs have been transferred to the holdingregisters at the end of a sample interval, then the remainingcalculations needed to determine the phase angle take place during thenext sampling interval in the background, while the accumulation for thenext pair is taking place in the foreground. These background routinesmust also have a way of determining on which pair of accumulated productterms they are working. A separate counter identifier is used for thesebackground routines which operates in a similar fashion to the counteridentifier for the front-end sampling interrupt. However, it is possibleto use the same counter, since this identifier will always be one countbehind the counter identifier for the front-end module samplinginterrupt routine.

The meter 34 illustrated in FIGS. 2, 3, 17A-B and 18A-B, into which thesystem 20 of the present invention is preferably integrated, is a solidstate single function KW/Kwh meter utilizing digital sampling techniquesto provide conventional Kw/Kwh demand, time of use, and otherconventional real time billing information in addition to the diagnosticinformation generated by the system 20 of the present invention. Themeter 34 is preferably programmed using software that runs on an IBMcompatible personal computer using the MS-DOS operating system. Thissoftware includes the logic for prompting the user to provide meterconfiguration parameters and preferably includes the installationprompts which provide for user-defined parameters for the diagnosticssupported by the system 20 of the present invention, so that a hand-heldpersonal computer can be plugged into a communications port on the meterto program the meter at installation.

FIGS. 17A-B illustrate the front-end module 44 of the meter 34 intowhich the system 20 of the present invention is preferably incorporated.The front-end module 44 preferably includes a Motorola MC68HC11KA4microprocessor 140 running in single chip mode, an integral 8-bit A/Dconverter 142, which serves as the voltage converter 26 in the system 20of the present invention, 24K bytes read only memory (ROM), 640 byteselectrically erasable programmable read only memory (EEPROM), and 768bytes random access memory (RAM), all shown at 144. The ROM and EEPROMinclude the diagnostic logic, and the RAM serves as storage memory forthe present invention. An external 12 bit A/D converter, shown at 146serves as the current A/D converter 28 for the system 20 of the presentinvention.

An additional error condition alert function may be implemented as anoption on the front-end module 44. This function utilizes a line out to,for example, an external communication device, which can be activatedwhenever an error condition is determined. This optional function may beutilized by the system 20 of the present invention for activating andcommunicating the existence of error conditions for any one of thediagnostics performed by the system 20 of the present invention.

An option board 146 may be incorporated into the front-end module 44 toprovide various signals to the outside world. For example, the errorcondition alert may be assigned to a low current solid-state orMercury-wetted relay to indicate when one or more diagnostic errors havebeen determined. Other known ancillary functions, such as automatedmeter reading or real time billing, may be implemented on option board146, or on a similarly configured option board utilized with thefront-end module 44.

Referring now to FIGS. 18A-B, the register module 48 of the meter 34into which the system 20 of the present invention is preferablyincorporated, includes a NECuPD75316GF single chip microprocessor 148,including 16K bytes of ROM, shown at 150, 512×4 bits of RAM, shown at152, and a 96 segment LCD display driver 154, suitable for driving anLCD display 156 such as the particular type of display 33 shown in FIG.3 and utilized in the preferred embodiment of the meter 34.

Serial data will be transferred between the front-end module 44 and theregister module 48 via a four wire synchronous serial data link shownrespectively at 158 in FIGS. 17A-B and 160 in FIGS. 18A-B. The front-endmodule will monitor and update the status of all of the diagnosticsperformed by the system 20 of the present invention and, periodically(preferably once per second) communicate these statuses to the registermodule 48 via the above-described serial communications link fordisplay, as well as for storage of volatile data in the event of a poweroutage. In addition, any instantaneous quantity required for display inthe Toolbox display of the present invention, will be communicated bythe front-end module as needed to the register module. The front-endmodule 44 also communicates various other conventional meter informationto the register module 48, such as the amount of energy (in Kwh)registered for the past 60 line cycles, as well as its direction(delivered or received), present demand and end-of-interval information.

Information which may be communicated from the register module 48 to thefront-end module 44, typically includes periodic meter register statusinformation.

Referring again to FIGS. 17A-B, the front-end module 44 enables themeasurement of per-phase voltage, current and watts for one sampleinterval (60 line cycles). As previously described, the front-end modulepreferably performs 481 samples per 60 line cycles, which corresponds to481 Hz when the line frequency is 60 Hz, and approximately 401 Hz whenthe line frequency is 50 Hz. The sampling frequency is recalculatedevery 60 cycles, based on the measured line frequency. As previouslydescribed, the diagnostic functions of the present invention, includingdetermination of instantaneous per-phase current, voltage, watts andphase angle, are preferably performed by the front-end module 44 whenthe system is incorporated in a meter of the type shown in FIG. 3.

Referring again to FIGS. 3 and 18A-B, the register module 48 preferablyperforms the function of driving the LCD display 33 in the meter 34. Aspreviously described, the Toolbox display of the present invention maybe implemented by activating an alternate display switch (not shown) fora predefined period. When activated, the Toolbox display mode isactivated and the display will scroll through the Toolbox display listas previously described herein. During a Toolbox display, the "TEST"icon preferably flashes continuously, and the watt disk emulator, shownas the five rectangular icons at the bottom of the display 33, willscroll at a rate of about one revolution per 1.33 seconds. The directionof the watt disk emulator will be the same as the direction of powerflow for the phase being displayed (left to right if received, right toleft if delivered). The meter will leave the Toolbox display mode whenthe end of the display is reached and the alternate display switch is nolonger activated. It should be noted, as previously described, the meterwill continue to perform all normal mode meter operations while theToolbox display sequence is active.

When the alternate display switch is not activated, the meter display 33operates in normal display mode for the meter 34.

Communication to or from the meter may also be accomplished through thefront-end module 44 via connection to the optical port 162.

Thus, the integral electronic meter system diagnostic package of thepresent invention provides the capability for continuous self-checkingof the internal components of the meter, as well as alert fieldpersonnel to any discovered error, without interruption of the meter'soperation. The system also provides the capability for constant systemdiagnostic checks, and display of those diagnostic results, to providepertinent diagnostic data to system personnel during or followinginstallation of the meter.

The system provides the flexibility of allowing the user to program thesystem to select and define the functions and parameters suitable to theparticular service supported by the meter installation.

Finally, the Toolbox display capability of the present invention allowsfor periodic display of valuable information respecting the internalfunctioning of the meter as well as the character of the servicesupported by the meter, again without interruption of normal service andmeter operation.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

What is claimed is:
 1. An electronic meter checking an electrical systemdiagnostics package including:a microprocessor; storage memory suitablyconnected to the microprocessor; logic for automatically periodicallyperforming a preselected test of meter checks and recording any errorsdetected therefrom; logic for automatically periodically performing apreselected series of system diagnostics tests and recording any resultswhich exceed predefined thresholds; display means for displaying errormessages identifying one or more errors discovered as a result of themeter checks performed during a predefined period; and display means fordisplaying diagnostic messages identifying any errors discovered as aresult of the system diagnostics tests performed during a predefinedperiod.
 2. The system of claim 1 further including logic forautomatically determining the type of electrical service in which themeter is installed.
 3. The system of claim 2 wherein the logic forautomatically determining the type of electrical service in which themeter is installed performs such determination during initialization ofthe meter upon installation of the meter.
 4. The system of claim 3wherein the logic for automatically determining the electrical servicein which the meter is installed performs such determination uponreconfiguration of the meter.
 5. The system of claim 2 wherein the logicfor determining the electrical service in which the meter is installedautomatically periodically performs such determination during normaloperation of the meter.
 6. An electronic meter system checking andtroubleshooting package for ascertaining voltage information from apolyphase electrical system metered thereby, including:(a) amicroprocessor; (b) storage memory suitably connected to saidmicroprocessor and (c) logic for automatically determining the type ofpolyphase electrical system in which a meter including the systemchecking and troubleshooting package is installed.
 7. The system ofclaim 6, further including logic for ascertaining voltage informationfrom the polyphase electrical system metered thereby.
 8. The system ofclaim 7, wherein said logic for ascertaining voltage information fromthe polyphase electrical system metered thereby includes logic fordetermining the phase angle of at least one voltage phasor of thepolyphase electrical system metered thereby relative to a selected basevoltage phasor, and wherein the logic for automatically determining thetype of polyphase electrical system in which the meter including thesystem checking and troubleshooting package is installed includes logicfor comparing the voltage phase angle of the at least one phasorrelative to the selected base phasor to a set of preselected voltagephasor angles for different possible types of electrical services, anddetermining the type of electrical service, if any, as a function of thevoltage phasor angle.
 9. The system of claim 8 wherein the logic fordetermining the type of electrical service makes such determination onthe basis of the angle between the C phase voltage phasor, V_(c), andthe A phase voltage phasor, V_(a), as well as the predefined form factorof the meter.
 10. The system of claim 9 wherein the logic fordetermining the phase angle of at least one phasor relative to aselected base phasor includes logic for storing accumulated digitalvalues corresponding to the instantaneous voltage measured for the basephasor X_(B), storing the accumulated digital values corresponding tothe instantaneous value measured for another selected phasor, X_(N),determining, for a predefined period, the RMS values for X_(B) andX_(N), denoted X_(B)(RMS) and X_(N)(RMS), respectively, determining theproduct, P, of X_(B)(RMS) and X_(N)(RMS), determining the average value,Q, of the product of the two sine waves corresponding to X_(B) andX_(N), and determining the average value, Y, of the product of the twosine waves corresponding to a shifted version of X_(B), denotedX_(B)(-90).
 11. The system of claim 10 wherein the logic furtherincludes logic for determining the magnitude of the phase angle of onephasor relative to the selected base phasor, θ, equal to arccos (Q/P).12. The system of claim 11 wherein the base phasor, X_(B), is the Aphase voltage phasor, and wherein the other selected phasor, X_(N), isthe C phase voltage phasor.